1. Field of the Invention
The present invention relates to the field of an image displays. More particularly, to a method and apparatus for reducing power consumption in an electronic equipment using a self-emitting type display.
2. Description of the Related Art
In recent years, display devices having various forms and uses have come into existence along with the rapid development of a computer and the spread of the Internet. These display devices are installed in a variety of electronic equipments ranging from equipments requiring somewhat large-size displays, such as a digital TV, a computer monitor, etc., to portable equipments requiring small and convenient displays, such as a portable phone, a Portable Digital Assistant (PDA), etc. However, particularly, because the portable equipments are supplied with power sources from rechargeable batteries, unlike the large size equipments, there is a very significant concern to increase a period of time of use of the smaller equipments by reducing the power consumption of the display portions of the device.
Conventionally, the display device can be classified into a transmissive display device, such as Liquid Crystal Display (LCD), and a self-emitting type display device, such as Plasma Display Panel (PDP), Organic Light Emitting Diode (OLED), etc.
As a part of the transmissive display device, the LCD receives white backlight from a backlight unit and passes or blocks out the backlight through a liquid crystal layer. The LCD controls a transmission ratio of the backlight by varying an alignment of the liquid crystal layer in response to voltages applied to electrodes provided on both surfaces of the liquid crystal layer. Transmitted light is converted into a color tone by a color filter and the colored light is emitted so as to be viewed by a user. In order to reduce power, the transmissive display device, such as the LCD, uniformly adjusts a brightness of a backlight light source irrespective of image information. This is because the backlight light source has the same power consumption regardless of whether a black color or a white color represents the image information.
As a part of the self-emitting type display device, the OLED (Optic Light Emitting Diode) is described regarding a light emitting principle. The OLED arranges electrodes on both surfaces of an organic thin film, forms excitons by exciting electrons and holes injected through the electrodes, and generates a specific-wavelength light using energy from the excitons. The self-emitting type display device can realize a full color by exhibiting Red, Green, and Blue (RGB) colors depending on the kind of organic matter included in the organic thin film. An intensity of light generated is purely determined by an intensity of a current supplied from a power source. Unlike the transmissive display device, the self-emitting type display device can enhance the efficiency of power consumption only through a reduction of a magnitude of an input signal because of a characteristic of a self-emitting device with no backlight. That is, the transmissive display device consumes constant power regardless of luminance, but the consumption power of self-emitting type display device is proportional to a flowing current. Because controlling brightness by an amount of a current, the self-emitting type display device consumes a lot of current when exhibiting high light. Thus, low power is essential in using the self-emitting type display device as a display of an electronic equipment, such as a portable phone. Further, simply collectively lowering a driving voltage for all signals of an image can deteriorate picture quality as a decrease of even a brightness of a user-unwanted part of the image may be problematic.